Electronic messaging services, including electronic mail, voice mail and digital facsimile (or fax), are common in today's business and home environments. Electronic messaging is a powerful communications tool that enables users to exchange information and collaborate across great distances and disparate time zones. Electronic messaging systems typically allow users to exchange messages over a network, including a common local area network (LAN) and an external network (e.g., the Internet). Electronic messaging systems also typically allow users to save, copy, and forward received messages. Many electronic messaging systems provide universal or unified messaging services for handling arbitrarily complex multimedia objects. For example, the Xpressions™ unified messaging system (available from Siemens Information and Communication Networks, Inc. of Boca Raton, Fla., U.S.A.) provides unified messaging services for handling voice mail, fax, e-mail and other types of electronic media. The Xpressions™ system provides an all-in-one mailbox (or personal message) center that users may access with a computer or a telephone to manage their messages.
A wide variety of digital content types may be transmitted through today's electronic messaging systems. A substantial amount of digital content, however, is subject to certain access restriction conditions. For example, some digital content (e.g., copyrighted works, such as textual works, musical works and video works) may not be copied or transmitted without the authorization of the copyright owner. Other digital content (e.g., proprietary works, confidential works and for internal use only works) may be copied and transmitted, but only a limited number of people may be authorized to have access to that content.